trigger calculateDMDTrigger on Contact (after delete, after insert, after undelete, after update) 
{

    Contact[] cons;
    if (Trigger.isDelete) 
        cons = Trigger.old;
    else
        cons = Trigger.new;

    // get list of accounts
    Set<ID> acctIds = new Set<ID>();
    for (Contact con : cons) 
    {
            acctIds.add(con.AccountId);
    }
    
    Map<ID, Contact> contactsForAccounts = new Map<ID, Contact>([select Id,
                                              	AccountId
                                              	from Contact
                                              	where AccountId IN :acctIds and Sub_Type__c 
                                              	IN ('DMD', 
                                              	'DCD')]); //

    Map<ID, Account> acctsToUpdate = new Map<ID, Account>([select Id,
                                                Active_DVA_DCD__c 
                                                from Account
                                                where Id IN :acctIds]);
                                                                 
    for (Account acct : acctsToUpdate.values()) 
    {
        Set<ID> conIds = new Set<ID>();
        for (Contact con : contactsForAccounts.values()) 
        {
            if (con.AccountId == acct.Id)
                conIds.add(con.Id);
        }
        if (acct.Active_DVA_DCD__c != conIds.size())
            acct.Active_DVA_DCD__c = conIds.size();
    }

    update acctsToUpdate.values();

}